Conventionally, an electrode assembly (including a cathode assembly, an anode assembly and a bipolar electrode) that includes a current collector having electrode layers (active material layers for cathode and anode) of generally uniform thickness on both sides of the current collector is used as the electrode assembly in secondary batteries, etc. Japanese Patent Application Publication No. 2005-149893 (JP-A-2005-149893) and Japanese Patent Application Publication No. 2004-179053 (JP-A-2004-179053) describe such a current collector.
Japanese Patent Application Publication No. 2005-11660 (JP-A-2005-11660) describes a secondary battery including electrode assemblies that each have a current collector on which a plurality of minute cells (electrode parts) forming an electrode layer are formed to relieve stress thereon. More specifically, a plurality of minute cells is arranged at regular intervals in a matrix on the current collector.
In the secondary battery described in JP-A-2005-11660, however, the following problems occur because the electrolyte layers are located only between minute cells on successive secondary battery electrodes in the stacking direction.
In the configuration described in JP-A-2005-11660, the regions without the minute cells on the current collectors are exposed, and the exposed portions are opposed to each other with a space therebetween. When the secondary battery receives an external force or when the secondary battery expands or contracts while being charged or discharged, the exposed portions of the current collectors may be deformed toward each other.